N form and concentration: Effects on reproductive development, growth and N content of southern peas¹

Contribution of the Georgia Agricultural Experiment Station and portion of a thesis submitted by the senior author in partial fulfillment of the requirement of the M.S. degree. This work was supported by Hatch 556 and by a grant from the Wilson and George Meyer Company.

Abstract

Southern peas [Vigna unguiculata, (L.) Walp.] cultured with 100% NH⁺ ₄ produced no viable flowers, while treatments in which NO^‐ ₃ composed 50% or more of the N form were not significantly different in the number of flowers formed. Flower abortion was least with 100% NO^‐ ₃ at the lower N concentration and with 75% and 100% NO^‐ ₃ at the higher N concentration. Further increments of NH⁺ ₄ resulted in greater flower abortion. The trends in flower survival were reflected in the number of pods and number of seed/plant. At the lower N concentration, the addition of NH⁺ ₄ slowed pod maturity, while at the higher N concentration pod maturity was hastened with the addition of up to 50% NH⁺ ₄. The dry weight and N content of tissues were generally greater with the higher N concentration and with N combinations containing predominantly NO^‐ ₃, but trends varied with the plant part being analyzed. Ammonium appears to adversely influence reproductive development and/or NO^‐ ₃ is essential to complete the reproductive development of southern peas. The observed differences in the response of southern peas to N form may account for previously reported discrepancies concerning the effectiveness of N fertilization on growth and yield parameters. Also, vegetative growth and vegetative N content appear to be poor indicators of final seed yields of southern peas if NH⁺ ₄ supplies a significant portion of the N form utilized by the plant.

Key words:

• Vigna unguiculata
• (L.) Walp.
• N nutrition
• solution culture

Notes

Contribution of the Georgia Agricultural Experiment Station and portion of a thesis submitted by the senior author in partial fulfillment of the requirement of the M.S. degree. This work was supported by Hatch 556 and by a grant from the Wilson and George Meyer Company.

Graduate student and Assistant Professor, respectively, Department of Horticulture, University of Georgia, Athens, Georgia 30602.